1. Field of the Invention
This invention relates a system for converting mechanical vibration signals to electrical signals in an electromagnetic type cartridge, and more particularly to a converting system wherein magnetic flux directly cuts coils in a manner such that in the vibration system there is used a simple construction such as the moving magnet type or induced magnet type and in the converting system there is not used such medium as pole pieces.
2. Description of the Prior Art
Transducer systesm may be classified into two kinds in which one is concerned with moving magnet type (hereinafter called as "MM Type") or induced magnet type (hereinafter called as "IM Type") and the other type is concerned with moving coil type (hereinafter called as "MCType").
The former type, namely, MM Type or IM Type is such a system that magnetic flux from the magnet or magnetic permeability material is vibrated, corresponding to which pole pieces are arranged, and a magnetic circuit is formed with the pole pieces so that a coil may sense the change in increase or decrease of the magnetic flux to induce voltage in the coil. In other words, a magnet or an armature is forced to thereby be vibrated, by which the change in magnetic flux is firstly transmitted to the pole pieces, through which voltage is induced in the coil.
The MC type cartridge is a system such that a coil itself is forced to be moved in a constant magnetic flux density to cut directly the magnetic flux without any medium.
Comparing these two systems in advantagous points and disadvantages respectively, in the former, the mechanical vibration system comprises only a magnet or an armature, a contilever and a stylus tip to thereby make the construction simple and to enable the effective mass of a stylus tip to be reduced Further, this type has the advantage that a high output voltage may be taken in that the number of windings can be increased. This type cartridge is, accordingly, mainly used in an electromagnetic type cartridge and widely used both in high class and popular class. However, in converting from mechanical signals to electrical signals, such an intermedium as pole pieces is inevitably used as aforementioned, through which an output voltage is induced in a coil. The coil voltage is, however, influenced by the magnetostriction or frequency characteristics of the magnetic material of the pole pieces to thereby make it impossible to convert with highfidelity from mechanical vibration signals to electrical signals and hence this type cartridge has the disadvantage that re-produced sound of high-fidelity is unable to be obtained.
On the other hand, in the latter type cartridge in which a coil formed integrally with a stylus cantilever is placed in magnetic filed having a constant magnetic flux density and is so arranged as to cut at a right angle the magnetic flux of direct current magnetic field, there is the advantage that output voltage may be induced in the coil with high fidelity in accordance with the movement of the coil due to the absence of an intermedium such as pole pieces which would cause a distortion or undesired influence between the coil and the direct current magnetic field. In other words, due to the conversion directly from mechanical vibration signals to electrical signals, this type has the merit that hi-fi reproduced sound is obtainable. However, the disadvantage exists that the mechanical impedance of a stylus tip necessarily increases owing to the complication of the mechanical vibration system because the coil itself is vibrated. In addition, the number of windings can not virtually increase so that high output voltage is not obtainable, which results in requiring a booster transformer for practical operation. This type has a further disadvantage that the stylus may not be replaced due to the coil being integrally formed in the mechanical vibration system and that the number of manufacturing process inevitably increases to increase accordingly the cost of the product. Therefore, this type is now used only in high-class of product.